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Stars, Galaxies, and the UniverseChapter 2
StarsSection 1 Vocabulary
◦Spectrum◦Apparent Magnitude◦Absolute Magnitude◦Light-Year◦Parallax
Color of StarsRed and Yellow
◦ CoolBlue
◦ WarmBlue flame hotter
than yellow flame
Stars different color
Betelgeuse-RedRigel-Blue
Composition of SlidesDifferent elements of
gasesInner Layers
◦ Very dense and hotOuter Layers
(Atmosphere)◦ Cool Gases
Elements in a star’s atmosphere absorb some of the light that radiates from the star.
Different wavelengths- different elements
The Colors of LightThe band of color
produced when white light passes through a spectrum
Millions of colors-rainbow
Continuous spectrum-shows all color◦ Glowing wire
Spectrograph◦ Break star’s light into a
spectrumComposition and
Temperature◦ Neon sign
Making and IDNeon SignEmission lines-lines
that are made when certain wavelengths of light, or colors, are given off by hot gases.
When an element emits light, only some colors in the spectrum show up, while other colors are missing.
Unique set of bright emission lines◦ Fingerprints
Trapping the Light-Cosmic Detective WorkStars produce
spectrumsDark emission
linesA star’s
atmosphere absorbs certain colors of light in the spectrum, which causes black lines to appear.
Identifying Elements Using Dark Lines
Absorption Spectrum- produced when light from a hot solid or dense gas passes through a cooler gas
A star gives off an absorption spectrum because a star’s atmosphere is cooler than the inner layers of the star.
The black lines represent places where less light gets through.
Identifying Elements Using Dark LinesThe pattern of
lines in a star’s absorption spectrum shows some of the elements that are in the star’s atmosphere.
One element-Easy
More than one element- hard
Classifying Stars1800’s-
astronomers started to collect and classify the spectra of many stars.
Classified according to the elements
Classified in the wrong order
Differences in in TemperatureHow hotTemperature
differences between stars result in color differences that you can see
O stars◦ Blue◦ Hottest
Highest temperature to lowest temperature
Differences in BrightnessEarly astronomers
created a system to classify stars based on their brightness.◦ First-magnitude –
brightest stars◦ Sixth-magnitude –
dimmest starsSome stars are too
dim to seeAdded to the old
systemPositive numbers-
dimmer stars
Apparent MagnitudeThe brightness of a
star as seen from Earth
Depends on the square of the ratio between the light and the light meter
Some stars are brighter than other stars because of their size or energy output, not because of their distance from Earth.
Absolute MagnitudeThe brightness a star
would have at a distance of 32.6 light years away
If all stars were the same distance away, their absolute magnitudes would be the same as their apparent magnitudes.
Sun- ◦ Absolute Magnitude
+4.8 Ordinary
◦ Apparent Magnitude -26.8 Brightest object in the sky
Distance to the Stars Light-Years to measure
distances from Earth to the stars
Stars near the Earth seem to move, while more distant stars seem to stay in one place as earth revolves around the sun.
Parallax-an apparent shift in the position of an object when viewed from different locations◦ Location of the nearer star
seems to shift in relation to the pattern of more distant stars
◦ Only seen through telescopes◦ Parallax and simple
trigonometry to find actual distances
Motions of the StarsDaytime and
Nighttime caused by rotation
Each season-faces different parts of the sky
Different set of constellations
The Apparent Motion of StarsSun appears to
move across the sky
Look long enough, the star appear to move
PolarisAppear to make
one complete circle around Polaris
The Actual Motion of StarsMoving in spaceDistance makes
it hard to seeStar pattern
slowly change their shape
The Life Cycle of StarsSection 2 Vocabulary
◦Red Giant◦White Dwarf◦H-R Diagram◦Main Sequence◦Supernova◦Neutron Star◦Pulsar◦Black Hole
The beginning and End of StarsFirst Stage- ball of gas
and dustGravity pulls it
together into a sphereMore Dense- HotterNuclear Fusion-
Hydrogen changes to Helium
Older-lose some materials
Materials returns to space
Forms new stars
Different Types of StarsStars can be
classified:◦ Mass◦ Brightness◦ Color◦ Temperature◦ Spectrum◦ Age
Types of stars:◦ Main-sequence◦ Giants◦ Supergiants◦ White Dwarf
Classifications can change.
Main-Sequence StarsSecond and
Longest StageEnergy is
generated in the core of the star as hydrogen atoms fuse into helium atoms
Releases an enormous amount of energy
Giants and SupergiantsThird stage of lifea large, reddish star
late in its life cycleLoss of hydrogen
causes center of the star to shrink
Atmosphere of the star grows very large and cools
Red giants- 10 times bigger than the sun
Supergiants- 100 times bigger than the sun
White DwarfsFinal Stages-Same mass as the sun
or smallerA small, hot, dim star
that is the leftover center of an old star
No hydrogen left and can no longer generate energy by fusing hydrogen atoms into helium atoms
Can shine billions of years before cooled
A Tool for Studying Stars1911-Hertzsprung
compared the brightness and the temperature of stars on a graph
1913-Russell made some similar graphs ◦ Different data- same
resultsHertzsprung –Russell
Diagram H-R Diagram
Tool for studying the lives of stars
Reading the H-R DiagramTemperature is on
the bottomAbsolute Magnitude
is on the left sideBlue stars on the left Red stars on the
rightBright stars on the
topDim stars on the
bottomMain sequence
◦ Most of the lifetime
When Stars Get OldDo not stay on the
main sequence forever
Average stars- red giants then white dwarfs
Stars that are larger than the sun- may explode◦ Supernovas◦ Neutron stars◦ Pulsars◦ Black holes
SupernovasBlue stars
◦ use their hydrogen much faster than stars like the sun
◦ generate more energy that stars like the sun
◦ Do not have long livesMay Explode
◦ Supernova◦ Brighter than an
entire galaxy for several days
Neutron Stars and PulsarsNeutron Star
◦ After a supernova Material in the center are
squeezed together to form a new star
About two times the mass of the sun
The particles are forced together to form neutrons
Pulsars ◦ Neutron Star spinning◦ Sends out a beam of
radiation that spins rapidly
◦ Beam is detected on Earth by radio telescopes as rapid clicks or pulses
Black HolesThe leftovers of a
supernova are so massive that they collapse to form a black hole
Do not give off light, finding them is difficult
If a star is nearby, some gas or dust from the star will spiral into the black hole and give off X-rays
GalaxiesSection 3 Vocabulary
◦Galaxy◦Nebula◦Globular Cluster◦Open Cluster◦Quasar
Types of GalaxiesMany Different
Types1920’s-classify
galaxies◦ By shape◦ Edwin Hubble
Still use the galaxy classification
Spiral GalaxiesBulge at the
centerSpiral Arms
◦ Gas, Dust, and New Stars
◦ Denser Regions of Gas and Dust
The Milky WayHard to tell what
type of galaxy◦ Gas, dust, and
stars keep astronomers from having a good view
They think it is a spiral galaxy.
Elliptical GalaxiesOne-third of all galaxies
are massive blobs of stars.
Elliptical Galaxies- bright centers and very little dust and gas
Contain mostly old stars
No to little free flowing gas
Giant elliptical galaxiesDwarf elliptical galaxies
Irregular GalaxiesGroup of
leftovers- “irregulars”
Do not fit into any other class
Shape-irregularLarge Magellanic
Cloud◦ close companions
of large spiral galaxies
Contents of GalaxiesComposed of
billions of stars and some planetary systems
Form large features◦ Gas clouds ◦ Star clusters
Gas CloudsNebulaLarge clouds of dust
and gasSome Glowothers absorb light
and hide starsOthers reflect starlight
and produce some amazing images
Some are regions that form new stars
Spiral-nebulasElliptical-very few
Star ClustersGlobular clusters-
groups of older stars◦ Up to one million stars◦ Located in a spherical
halo that surrounds spiral galaxies
◦ Common near giant elliptical galaxies
Open clusters-closely grouped stars◦ Located along the spiral
disk of a galaxy◦ Newly formed-many
bright blue stars◦ Few hundred to a few
thousand stars
Origin of GalaxiesObserving objects far
awayTakes time for light
to travel through space, looking through a telescope is like looking back in time
Shows what early galaxies looked like
How they change over time and what caused them to form
Formation of the UniverseSection 4 Vocabulary
◦Cosmology◦Big Bang Theory
Raisin-Bread Model Imagine a loaf of bread
before its bakedEach raisin is a certain
distance apartAs the dough rises, it
expands and all of the raisins begin to move apart
Other raisins are moving away from it
The universe is expanding
Raisins as galaxiesGalaxies move apart
The Big Bang TheoryWhat it would
look like in reverse
It look like it is contracting.
All matter would come together at a single point
Squeezed into one small space
A Tremendous ExplosionBig Bang Theory13.7 billion years ago-
all the contents of the universe was compressed under extreme pressure, temperature, and density in a very tiny spot
Rapidly expandedMatter began to come
together and form galaxies
Cosmic Background Radiation
1964- twos scientists using a huge antenna accidentally found radiation coming from all directions in space
Cosmic background radiation
Kitchen ovenBig Bang Theory- the
thermal energy from the original explosion was distributed in every direction as the universe expanded
Now fills all of space
Structure of the UniverseUniverse
stretches out farther than astronomers can see with their advanced instruments
Not simply scattered through the universe in a random pattern
Has structure
A Cosmic RepetitionPart of a larger
systemCluster or group of
galaxies can be made up of smaller star clusters and galaxies
Can include planetary systems
Other planets can be detected in orbit around other stars
common
How Old Is the Universe?One Way scientists
can calculate the age of the universe is to measure the distance from Earth to various galaxies
Estimate the age of the universe and predict its expansion
To calculate the ages of old, nearby stars
A Forever Expanding Universe
As they move farther apart they get older and stop forming stars
The expansion of the universe depends on how much matter the universe contains
Gravity could eventually stop expanding◦ Eventually start
collapsingNot enough matter
◦ Will continue to expand forever
◦ cold and dark
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